Cooking device for appropriately processing pre-cooked frozen food

ABSTRACT

After the initial temperature T0 of a heating chamber is sensed (S34), heating by microwaves is conducted until the sensor output of a humidity sensor exhibits a prescribed humidity change amount of 1.0 V (S35-S39). Then, an additional time period is operated based on initial temperature T0 and a time period passed for the elevation of 1.0 V (S40-S42, S50). Heating by microwaves is conducted for the additional time period (S43, S51), and then heating by a heater is conducted. As a result, the moisture included in the food is evaporated and finished crisp. In other words frozen precooked food may be thawed and cooked into a tasty state.

TECHNICAL FIELD

The present invention relates generally to cooking devices capable ofmicrowave-heating and heating with a heater, and more particularly to acooking device suitable for processing precooked food.

BACKGROUND ART

A cooking device of interest to the present invention is disclosed byJapanese Patent Laying-Open No. 4-225727. According to the patentapplication, the cooking device includes a heating chamber foraccommodating food to cook, a microwave heater and a heater for heatingfood placed in the heating chamber, a temperature sensor provided on thesurface of the wall of the heating chamber for sensing the temperaturewithin the heating chamber, an exhaust temperature sensor provided at anexhaust portion for letting out the atmosphere of the heating chamber, ahumidity sensor for sensing the humidity within the heating chamber anda controller for controlling the entire cooking device. By the functionof the controller, the microwave heater heats food until the outputchange amount of the humidity sensor reaches a prescribed value afterstarting heating, and then the heater heats the food for a calculatedtime period corresponding to the temperature change amount of theexhaust temperature sensor and heating time until the amount of humiditychange reaches a prescribed value after starting heating.

Generally, food is heated by microwaves until the change amount of thehumidity sensor reaches a prescribed value, and then the food isfinished cooking by evaporating moisture using the heater. The humiditysensor however has a limited sensitivity, and it would be difficult todetect the same condition as for various kinds of cooking. If the outputof the humidity sensor is the same, the state of heating is not alwaysthe same.

In order to solve such a disadvantage, there is a method of continuingmicrowave-heating while steaming the food wrapped with plastic wrap withvapor generated on the food. According to the method, the finished foodbecomes damp and the look is also spoiled. Therefore, after heating foodby microwave heating without using wrap, evaporating the food by heatingwith a heater such as electric heater in order to make the finished foodcrisp and look delicious.

Recently, consumers use more frozen precooked food such as frozen pilafand frozen prefried food sold at convenience stores. These kinds of foodare thawed, heated and then served at tables of households. The foodoften becomes damp and looks tasteless.

The above-described method is directed to solving such a disadvantage,but the method is still encountered with the following problem.

Among various kinds of frozen precooked food, each item of frozenprefried food has a small unit value, through which microwaves easilypenetrate, and therefore, thawing and heating progress quickly.Meanwhile, it is hard for microwaves to penetrate to the center of foodsuch as frozen pilaf and frozen grilled rice balls in a large lump, andtherefore, heating of the center of the food progresses slowly.

Therefore, frozen pilaf and frozen grilled rice balls in a large lumpare thawed starting from the surface portion in the progress of heating.As a result, the output of the humidity sensor changes as the heating ofthe surface of the food proceeds. If therefore, the change amount of thehumidity sensor reaches a prescribed value, the center of the food isnot thawed enough and not heated enough unlike the surface. If the foodis subjected to following heating with the heater with its center stillnot heated enough, the thawing of the center proceeds by the heatemitted from the heater. The moisture generated by the thawing oozesonto the surface, and the surface of the food finished cooking becomesdamp and tasteless.

It is therefore an object of the present invention to provide a cookingdevice capable of appropriately processing precooked food, whichovercomes the disadvantage associated with such a conventional cookingdevice.

DISCLOSURE OF THE INVENTION

A cooking device according to the present invention includes a heatingchamber for placing food, a microwave heater for heating the food in theheating chamber with microwaves, a heater for heating the food withinthe heating chamber, a temperature sensor for sensing the temperaturewithin the heating chamber, a humidity sensor for sensing the humidityof the heating chamber, a controller making such a control that themicrowave heating by the microwave heater is followed by heating by theheater, and a timer portion for counting time until the sensor output ofthe humidity sensor exhibits a prescribed humidity change from the startof heating. The controller controls the microwave heater to performadditional heating in response to the counting result of the timer andthe temperature detected at the start of heating.

Since such additional heating is conducted by the microwave heater basedon the time required for a prescribed humidity change and thetemperature at the start of heating, the surface of food does not becomedamp by the moisture emitted from the center of the food not yet thawed.As a result, the thawed food may be cooked into a beautiful taste.

The controller preferably calculates an additional time period based onthe result of counting by the timer and the temperature of the heatingchamber at the start of heating which is detected by the temperaturesensor.

The additional time period is calculated based on heating time until thehumidity sensor exhibits a prescribed humidity change, the microwaveheater heats the food for the additional time period, and therefore, thefood is heated for an appropriate additional time period.

According to another aspect of the invention, the cooking deviceincludes a heating chamber for placing food, a microwave heater forheating the food in the heating chamber, a heater for heating the foodin the heating chamber, a temperature sensor for sensing the temperaturein the heating chamber, a humidity sensor for sensing the humidity inthe heating chamber, a first cooking course execution portion forexecuting a first cooking course of heating the food with the microwaveheater until the output of humidity sensor exhibits a prescribedhumidity change from the start of heating followed by heating by theheater, a second cooking course execution portion for executing a secondcooking course of performing additional heating based on a temperaturesensed by the temperature sensor at the start of heating and a timeperiod until the sensor output of humidity sensor exhibits a prescribedhumidity change from the start of heating between the heating by themicrowave heater and the heating by the heater in the first cookingcourse, and a selection portion for selecting one of the first cookingcourse and the second cooking course.

Since the first cooking course or the second cooking course may beselected based on food to cook by heating, a cooking device capable ofperforming appropriate heating based on the kind of food is provided.

The selection portion preferably selects the first cooking course if theamount of humidity change sensed by the humidity sensor after aprescribed time period is passed from the start of heating is largerthan a prescribed cooking determination value, and selects the secondcooking course if the amount of humidity change is smaller than thecooking determination value.

Since the selection portion automatically selects a cooking course basedon the amount of humidity change from the start of cooking to effect thefirst or second cooking course execution portion, appropriate heatingmay automatically be performed.

The cooking device more preferably includes an operation portion forinstructing the start of cooking and selection of a cooking course, andthe selection portion selects and effects the first cooking courseexecution portion or the second cooking course execution in response toan instruction from the operation portion.

Since the first or second cooking course execution portion is executedthrough the selecting portion in response to an instruction from theoperation portion, the user may select a desired cooking course.

More preferably, the food is frozen precooked food.

Since appropriate heating is conducted to frozen precooked food, acooking device capable of thawing such frozen precooked food into a goodtaste may be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overview showing a microwave oven according to oneembodiment of the present invention;

FIG. 2 is a control block diagram for the microwave oven;

FIG. 3 is a flow chart showing the operation of a cooking deviceaccording to the present invention;

FIGS. 4 and 5 are flow charts showing the operations of cooking coursesfor fried food and pilafs;

FIGS. 6 to 8 are flow charts showing the operation of cooking pilaf;

FIG. 9 is a graph showing the relation between the sensor output of ahumidity sensor and passage of time;

FIG. 10 is an overview showing a microwave oven according to anotherembodiment of the invention;

FIG. 11 is a control block diagram for a microwave oven according toanother embodiment of the invention;

FIG. 12 is a flow chart for use in illustration of the operation of amicrowave oven according to another embodiment of the invention;

FIGS. 13 to 15 are flow chats for use in illustration of a precookedfood cooking course shown in FIG. 12; and

FIG. 16 is a graph showing the relation between the sensor output of thehumidity sensor and passage of time.

PREFERRED EMBODIMENTS FOR IMPLEMENTING THE INVENTION

The present invention will be more specifically described in conjunctionwith the accompanying drawings.

Referring to FIG. 1, a microwave oven 1 having a function ofoven-cooking according to one embodiment of the invention includes anoperation portion 2 provided at the front surface of microwave oven 1.Operation portion 2 has a start key 3 functioning both to select awarming course and to instruct starting of cooking, a cooking selectiondial 4 provided around start key 3 for selecting an automatic cookingmenu by turning, a first key 5 for cooking frozen prefried food/pizzasamong various kinds of frozen precooked food, and a second key 6 forcooking frozen pilaf (as well as frozen grilled rice ball). The firstkey 5 and second key 6 form the selection portion of the controllerwhich will be described later.

Microwave oven 1 includes a heating chamber 7 for accommodating food 8,a magnetron 9 functioning as a microwave heater for heating food 8 inheating chamber 7 by microwaves radiated from an antenna 9a, an upperheater 10 mounted on the upper wall of heating chamber 7, a lower heater11 mounted on the lower wall of heating chamber 7, a turn table 12 forturning food 8 placed thereon in heating chamber 7, and a turn tablemotor 13 for turning turn table 12. Upper heater 10 and lower heater 11heat food 8. The heaters may be a convection type heater.

Microwave oven 1 is provided with a cooling fan 14, which lets in theair through the inlet 15 (not shown) of microwave oven 1 and cools themagnetron 9 and the controller which will be described later. Inlet 15is provided at the sidewall 7a of heating chamber 7 on the side ofcooling fan 14 and introduces cooling wind into heating chamber 7. Anexhaust outlet 16 is provided at side wall 7b on the side opposite toside wall 7a. The direction in which the atmosphere from heatingchambers 7 is exhausted from exhaust outlet 16 is changed downward bythe function of an exhaust duct 17. Exhaust duct 17 is provided with ahumidity sensor 18 for sensing the humidity of the atmosphere let outfrom heating chamber 7. An outer exhaust outlet 19 is provided at theside wall of microwave oven 1, and a thermistor 20 functioning as atemperature sensor is provided on the upper wall of the heating chamber7.

Note that food 8 is placed in heating chamber 7 from the opening in thefront and enclosed therein by a door (not shown) which opens/closes.

FIG. 2 shows a controller 21 formed of a microcomputer. Controller 21 isconnected with operation portion 2, magnetron 9, upper heater 10, lowerheater 11, turn table motor 13, cooing fan motor 14, humidity sensor 18and thermistor 20.

Controller 21 has an initial temperature sensing portion 22 for sensingtemperature T0 in heating chamber 7 at the start of heating usingthermistor 20, a humidity change detection portion 23 for detecting ahumidity change from the start of heating based on the sensor output ofhumidity sensor 18, a humidity change timer portion 24 functioning as atimer for counting a time period until a prescribed humidity change fromthe start of heating is obtained at humidity change detection portion23, an additional heating portion 25 for executing additional heating bymicrowave heating based on an output from humidity change timer portion24 and on temperature T0 detected by initial temperature detectionportion 22, a first cooking course execution portion 26 for executingcooking as shown in FIGS. 4 and 5 which will be described later inresponse to an operation of first key 5, a second cooking courseexecution portion for executing cooking as shown in FIGS. 6 to 8 whichwill be described later in response to an operation of second key 6, anda memory 28.

Humidity sensor 18 is formed of open type and close type thermistorshaving the same temperature characteristics, and humidity is calculatedbased on the difference between temperatures detected by these twothermistors as a sensor output.

Now referring to FIGS. 3, the operation of the cooking device accordingto the present invention will be described. In step S1, a cooking flag(denoted as COOKING in FIGS. 3 to 8) and a menu flag (denoted as MENU inFIGS. 3 to 8) are reset to 0 in an initialization operation. In steps S2to S5, the operated key is determined.

More specifically, in step S2, it is determined if first key 5 wasoperated, and if it is determined that the key was operated, the cookingflag is set to 1 in step S6. In step S3, it is determined if second key6 was operated, and if it is determined that the key was operated, thecooking flag is set to 2 in step S7. In step S4, it is determined if theautomatic menu was selected by cooking selection dial 4, and if it isdetermined that the menu was selected, the menu flag is set to 1 in stepS8. In step S5, it is determined if start key 3 was operated, and if itis determined that the key was operated, the operation transits to thefollowing step, and if not, the operation returns to step S2. Note thatif it is determined in steps S2 to S5 that no operation was made, theprocessing transits to the following step in order.

If it is determined in step S5 that start key 3 was operated, in thefollowing steps S9 to S11, how each flag is set is determined in orderto select a method of controlling.

More specifically, it is determined if the cooking flag is set to 1 instep S9, and if the flag is set to 1, the frozen precooked food heatingcourse for fried food/pizzas is executed in the first cooking courseexecution portion 26 of controller 21. If it is determined in step S9that the flag is not set to 1, the processing transits to step S10, andit is determined if the cooking flag is set to 2, and if the flag is setto 2, in step S13 the frozen precooked food heating course for pilaf isexecuted in the second cooking course execution portion 27.

If it is determined in step S10 that the cooking flag is not set to 2,it is determined in step S11 if the menu flag is set to 1, and if themenu flag is set to 1, in step S14 a heating course for the cooking menuselected by selection dial 4 is executed. If it is determined in stepS11 that the menu flag is not set to 1, it is determined that only startkey 3 was operated and the warming heating course is executed in stepS15. If execution of any of the courses from steps S12 to S15 completes,the processing returns to step S1, executes an initialization operationand waits until the next operation.

Now, a description will follow on the operation of the frozen precookedfood heating course for fried food/pizzas described in step S12 shown inFIG. 3. In step S12, initial temperature T0 in heating chamber 7 isdetected in step S16, in other words the temperature in the heatingchamber 7 is sensed by initial temperature detection potion 22 using thethermistor 20. In step S17, magnetron 9 and cooling fan 14 are driven.In step S18, the humidity change timer portion 24 of controller 21starts counting passage of time from the start of heating. In step S19,it is determined if initial temperature T0 is lower than 151° C.

If it is determined that the temperature is lower than 151° C. in stepS19, in step S20 humidity change detection portion 23 determines if thesensor output of humidity sensor 18 has changed by 0.6 V from the startof heating, in other words the humidity change has reached 0.6 V. If itis determined in step S20 that the change of 0.6 V is reached, in stepS21 passage of time t1 counted by humidity change timer portion 24 isstored in the memory 28 of controller 21.

It is determined in step S22 if the above-described time t1 is 1 minuteor shorter. If passage of time t1 is equal to or shorter than 1 minute,the operation of magnetron 9 is stopped in step S23 and upper heater 10and lower heater 11 are turned on for 3 minutes and 10 seconds, thuscompleting the heating.

If passage of time t1 is equal to or longer than 1 minute, it isdetermined in step S24 if it is in the range from one minute to twominutes, and for the period equal to or less than two minutes, theoperation of magnetron 9 is stopped in step S25, and upper heater 10 andlower heater 11 are turned on for 3 minutes and 50 seconds, and thenheating with the heaters is completed.

If passage of time t1 is longer than two minutes, the operation ofmagnetron 9 is stopped in step S26, upper heater 10 and lower heater 11are turned on for 4 minutes and 20 seconds, thus completing heating withthe heaters.

If it is determined in step S19 that it is equal to or higher than 151°C., it is determined in step S27 if the output of humidity sensor 18 haschanged by 0.4 V from the start of heating. If it is determined in stepS27 that the change by 0.4 V was made, in step S28 a time period t1counted by humidity change counter portion 24 is stored in the memory 28of controller 21. Herein, the change amount of 0.4 V corresponds to aprescribed humidity change amount.

In step 29, it is determined if the above-described time period t1 isequal to or shorter than 1 minute. If t1 is equal to or shorter than 1minute, in step S30 the operation of magnetron 9 is stopped, upperheater 10 and lower heater 11 are turned on for 2 minutes and 40seconds, thus completing heating by the heaters.

If time period t1 exceeds 1 minute, it is determined in step S31 if thetime period exceeds one minute and equal to or shorter than to 2minutes, and if it is equal to or shorter than 2 minutes, in step S32the operation of magnetron 9 is stopped, upper heater 10 and lowerheater 11 are turned on for 3 minutes and 10 seconds, thus completingheating by the heaters.

If time period t1 exceeds 2 minutes, the operation of magnetron 9 isstopped in step 33, upper heater 10 and lower heater 11 are turned onfor 3 minutes and 35 seconds, thus completing heating by the heaters.

Once execution of any of the courses according to steps S23, S25, S26,S30, S32 and S33 completes, the processing in the precooked food heatingcourse for fried food/pizzas in steps S12 completes.

Now, operations in the precooked food heating course for pilaf shown instep S13 in FIG. 3 will be described in conjunction with FIGS. 6 to 8.

If the operation transits to step S13, in step S34 the initialtemperature T0 of heating chamber 7 is detected first. Morespecifically, the temperature in heating chamber 7 is detected byinitial temperature detection portion 22, using thermistor 20. In stepsS35, cooling fan 14 is driven. At the time, the counting operation ofhumidity change counter portion 24 in controller 21 for counting passageof time from the start of heating is initiated. In step S36, magnetron 9is driven. In step S37, it is determined if the humidity at humiditysensor 18 has changed by 0.1 V from the start of heating, using humiditychange detection portion 23. If it is determined in step S37 that thechange of 0.1 V was made, passage of time t1 at humidity change counterportion 24 is stored in memory 28 in step S38.

Then, heating by microwaves is continued until it is determined in stepS39 that the output of humidity sensor 18 has changed by 1.0 V from thestart of heating. If it is determined by humidity change detectionportion 23 in step S39 that the sensor output has changed by 1.0 V,passage of time t2 from the start of heating is stored in memory 28 instep S40, and the operation transits to the next step. Herein the changeamount of 1.0 V corresponds to a prescribed humidity change amount.

It is determined in step S41 if initial temperature T0 is lower than120° C. If it is determined in step S41 that the temperature is lowerthan 120° C., in step S42 time produced by multiplying time t2 by 0.6 isoperated to produce an additional heating time period, using additionalheating portion 25. In step S43, counting of the additional time periodby additional heating portion 25 is started and the operation transitsto the following step if the heating time is passed. In this additionalheating, magnetron 9, continues to be driven in order to execute heatingby microwaves.

Step S44 stops driving cooling fan 14. It is determined in step S45 ifthe above-described passage of time t1 is equal to or shorter than 2minutes. If time t1 is equal to or shorter than 2 minutes, the operationof magnetron 9 is stopped in step S46, upper heater 10 and lower heater11 are turned on for 1 minute and 15 seconds, and then the heating bythe heaters completes.

If time period t1 is longer than 2 minutes, it is determined in step S47if the time period is longer than 2 minutes and equal to or shorter than3 minutes and 15 seconds. If it is equal to or shorter than 3 minutesand 15 seconds, the operation of magnetron 9 is stopped in step S48,upper heater 10 and lower heater 11 are turned on for 1 minute and 45seconds, and then heating by the heaters completes.

If passage of time t1 is longer than 3 minutes and 15 seconds, theoperation of magnetron 9 is stopped in step S49, upper heater 10 andlower heater 11 are turned on for 2 minutes and 30 seconds, and thenheating by the heaters completes.

If it is determined in S41 that the temperature is not lower than 120°C., in other words equal to or higher than 120° C., in step S50 timeproduced by multiplying t2 by 0.8 is operated as an additional heatingtime period by additional heating portion 25. In step S51, counting ofthe additional heating time period by additional heating portion 25 isinitiated, and the operation transits to the following steps afterpassage of the heating time period. The additional time period isprovided to continue heating by microwaves by continuing to drivemagnetron 9.

In step S52, cooling fan 14 is stopped from driven. It is determined instep S53 if the above-described time t1 is equal to or shorter than 2minutes. If t1 is equal to or shorter than 2 minutes, the operation ofmagnetron 9 is stopped in S54, upper heater 10 and lower heater 11 areturned on for 50 seconds, and then heating by the heaters completes.

If time t1 is longer than 2 minutes, it is determined in step S55 if thetime period is longer than 2 minutes and equal to or shorter than 3minutes and 15 seconds. If it is equal to or shorter than 3 minutes and15 seconds, the operation of the magnetron 9 is stopped in S56, upperheater 10 and lower heater 11 are turned on for 1 minute and 15 seconds,and then heating by the heaters completes.

If time period t1 is longer than 3 minutes and 15 seconds, the operationof magnetron 9 is stopped in step S57, upper heater 10 and lower heater11 are turned on for 1 minute 30 seconds, and then heating by theheaters completes.

Once execution of any of the courses according to steps S46, S48, S49,S54, S56, and S57 completes, the frozen precooked food heating coursefor pilaf in step S13 completes.

Now, the operation started by operating second key 6 will be describedby illustrating specific examples. Herein, the temperature in heatingchamber 7 is at 20° C.

After food 8 is placed in heating chamber 7, second key 6 is operated.Controller 21 determines the operation in steps S3, and the cooking flagis set to 2. When a user operates second key 6 and then start key 3,controller 21 determines in step S10 that the cooking flag is set to 2,and the cooking course according to step S13 is executed. According tothe cooking course, initial temperature T0 in heating chamber is 7 isdetected by thermistor 20. The temperature detected in this case is 20°C. as described above, then, cooling fan 14 and magnetron 9 are drivenand it is determined in step S37 if the output of humidity sensor 18detected by humidity change detection portion 23 has changed by 0.1 V.

At the time, the output of humidity sensor 18 elevates with passage oftime from the start of heating as illustrated in FIG. 9. If the value iselevated to 0.1 V, time t1 is stored in memory 28 in step S38. Supposethat time period t1 is for example 2 minutes. If it is determined instep S39 that the output of humidity sensor 18 detected by humiditychange detecting portion 23 has changed by 1.0 V, a time period t2counted by humidity change counter portion 24 is stored in memory 28.Suppose that time period t2 is for example 5 minutes.

It is determined in step S41 that initial temperature t0 (20° C.) islower than 120° C., and the operation transits to step S42. In step S42an additional heating time period is operated by additional heatingportion 25. More specifically, 5×0.6=3 minutes results. Then in stepS43, counting of 3 minutes is initiated by additional heating portion25, and the operation transits to step S44 after the counting completes.Note that during this additional heating time period, heating by themicrowave continues.

If it is determined in step S43 that the additional heating time periodis passed, cooling fan 14 is stopped, and the operation transits to stepS45. Since time period t1 is set to 2 minutes as described above, it isdetermined in step S45 that the time period is equal to or shorter than2 minutes. In step S46 magnetron 9 is turned off, and upper heater 10and lower heater 11 are turned on. After heating by the heaterscontinues for 1 minutes 15 seconds, upper heater 10 and lower heater 11are turned off, thus completing execution of the cooking course.

Another embodiment of the invention will be described in conjunctionwith FIGS. 10 to 16. In the figures, the same portions as those in FIGS.1 and 2 are denoted with the same reference character and numerals, withdescription thereof being omitted.

Referring to FIG. 10, the cooking device is provided with a cooking key38 operated in order to heat frozen precooked food which will bedescribed later. A selection portion 29 is provided to selectivelyeffect a first cooking course execution portion 26 or a second cookingcourse execution portion 27 based on the amount of humidity changedetected by humidity change detection portion 23 for a prescribed timeperiod from the start of heating.

In this embodiment, as illustrated in FIG. 16, the amount of change ofhumidity of frozen precooked food such as pilaf is equal to or smallerthan 0.2 V 90 seconds after the start of heating regardless of theamount of the food, while the change is equal to or more than 0.2 V forfried food. Detecting the difference in change amounts permits automaticdetermination of the kind of frozen precooked food, in other words, ifit is fried food or pilaf, and cooking appropriate for the food isexecuted. Note that as for a smaller amount to heat, thawing is quicker,and the humidity changes quickly, while if the amount to heat is large,it takes more time for thawing, and the humidity changes slowly. Theenergy to heat food is therefore determined taking this into account.

The operation according to this embodiment will be described withreference to the flow charts shown in FIGS. 12 to 15. An initializationoperation is executed by setting the cooking flag (denoted as COOKING inFIGS. 12 to 15) and the menu flag (denoted as MENU in FIGS. 12 to 15) to0 in step S100. In steps S101 to S103, the key operated is determined.

More specifically, it is determined in step S101 if cooking key 28 wasoperated. If it is determined the key was operated, in step S104, thecooking flag is set to 1. In step S102 it is determined if the automaticmenu was selected by cooking selection dial 4. If it is determined thatthe dial was operated, the menu flag is set to 1 in step S105. It isdetermined in step S103 if start key 3 was operated. If it is determinedthat the key was operated, the operation transits to the next step, ifit was not operated, the operation returns step S101. Note that if it isdetermined that no operation was made from step S101 to step S103, theoperation transits to the next step.

If it is determined in step S104 that start key 3 was operated, how eachflag is set is determined in step S106 or S107 in order to select amethod of controlling.

More specifically, it is determined in step S106 if the cooking flag isset to 1. If the cooking flag is set to 1, the frozen food cookingcourse is executed in step S108. If it is determined that the flag isnot set to 1 in step S106, it is then determined in step S107 if themenu flag is set to 1. If the flag is set to 1, a course of heating acooking menu selected by selection dial 4 is executed in step S109. Ifit is determined in step S107 that the menu flag is not set to 1, it isdetermined that only start key 3 was operated, and the warming heatingcourse in step S110 is executed.

If execution of any of the courses according to steps S108 to S110completes, the operation returns to step S100, and waits until the nextoperation after executing an initialization operation.

The frozen precooked food cooking course in step S108 as described abovewill be detailed with reference to FIGS. 13 to 15.

When the operation transits to step S108, in step S111 magnetron 9 andcooling fan 14 are driven. Counting 10 of passage of time from the startof heating is initiated at humidity change counter portion 24 incontroller 21. In step S113, the operation waits until humidity counterportion 24 counts 90 seconds.

It is determined in step S114 if the output of humidity sensor 18 haschanged by 0.2 V or more by selection portion 29. If it is determined instep S114 that the change of 0.2 V or more was made, the first cookingcourse for heating fried food in step S115 and on is selected to executestart cooking course execution portion 26. Meanwhile, if it isdetermined that the change was not 0.2 V or more, the second cookingcourse for heating pilaf in step S126 and on is selected and the secondcooking course execution portion executes the processing. If the firstcooking course is selected, the operation waits until the humiditychange counter portion 24 counts 120 seconds since the selection wasmade is step S115. It is determined in step S116 if the amount ofhumidity change detected by humidity change detection portion 23 for the120 seconds is 0.3 V or longer. In this step, if the amount to heatfried food is large or small is determined.

If it is determined that the amount is 0.3 V or more in step S116, theamount of heat is determined to be small, and in step S117 the operationwaits until the result of the detection by humidity change detectionportion 23 becomes 0.8 V or more. In step S118, a time period from thestart of heating till humidity change detection portion 23 detects thechange amount of 0.8 V or more counted by humidity change counterportion 24 is stored as t in memory 28. In step S119, a heating timeperiod by the heaters is produced by the operation of 0.5×t.

If it is determined in the above step S116 that the change of 0.3 V ormore was not made, and that the amount to heat is large, the operationwaits until the amount of humidity change output at humidity changedetection portion 23 becomes 1.0 V. In step S121, a time period from thestart of heating till humidity change detection portion 23 detects thechange amount of 1.0 V or more is counted by humidity change counterportion 24 and stored in memory 28. In step S122, a heating time periodby the heaters is produced by the operation of 0.4×t.

In step S123 magnetron 9 and cooling fan 14 are turned off, upper heater10 and lower heater 11 are turned on, and heating by the heaters isexecuted. It is determined in step S124 if the heating time period bythe heaters produced in step S119 or S122 has passed.

If it is determined in step S124 that the heating time period by theheaters has passed, upper heater 10 and lower heater 11 are turned offin step S125, thus completing the heating cooking. The operation returnsto step S100, and waits until the next cooking is instructed.

If the second cooking course is selected in step S114, in other words,it is determined that the food to cook is pilaf because the output ofhumidify change detection portion 23 does not change by 0.2 V or moreduring the time period of 90 seconds counted, the operation waits untilhumidity change counter portion 24 counts 120 seconds since theselection in step S126. It is determined in step S127 if the amount ofhumidity change detected by humidity change detection portion 23 for the120 seconds is 0.35 V or more. In this step, it is determined if theamount of heat for pilaf is large or small.

If it is determined in step S127 that the amount of humidity change is0.35 V or more and that the amount of heat is small, in step S128, theoperation waits until the result of detection at humidity changedetection portion 23 becomes 1.0 V or more. In step S129 the time periodform the start of heating until the amount of humidity change detectedby humidity change detection portion 23 which is 1.0 V is counted byhumidity change counter portion 23 and stored in memory 28. In step 130,an additional operation time period in microwave heating is produced bythe operation of 0.5×t.

In step S131, heating by microwaves for the additional operation timeperiod produced in the above step is executed, and then magnetron 9 andcooling fan 14 are stopped in step S132, and then upper heater 10 andlower heater 11 are turned on for switching to heating by the heaters.

In step 133, heating by the heaters is executed for 3 minutes, and theheaters are turned off in step S125.

If it is determined in step S127 that the change of 0.35 V or more wasnot made, in other words, the amount of heat is large, in step S134 theoperation waits until the result of detection by humidity changedetection portion 23 becomes 1.0 V or more.

In step 135, the time period from the start of heating started countingby humidity change counter portion 23 till the amount of humidity changedetected by humidity change detection portion 23 reaches 1.0 V is storedin memory 28 as t. In step S136, an additional time period for heatingby microwaves is produced by the operation of 0.7×t.

In step S137, microwave heating for the additional operation time periodproduced in the above step is executed, then in step S138 magnetron 9and cooling fan 14 are stopped, and upper heater 10 and lower heater 11are turned on, thus switching to heating by the heaters.

In step S139, heating by the heaters is executed for 1 minute and 30seconds, and then the heaters are turned off in step S125.

Thus, the second cooking course completes, and the operation returns tostep S100 and waits until the next cooking is instructed.

As in the foregoing, frozen precooked food such as frozen pilaf andgrilled rice balls which are sold at convenience stores are thawed andheated, no such situations is encountered that they are not thawed tothe centers during heating by microwaves but thawed during heating bythe heaters and moisture in the centers comes onto the surface, dampingthe finished food. The finished food will be crisp and more tastyaccording to the present invention.

Note that the heating cooking according to the above-describedembodiment is designed to avoid the necessity of wrapping food withfilm, and therefore the user may enjoy economical advantage as well.

The additional time period operated by additional heating portion 25 inthe above-described embodiment is determined based on the initialtemperature T0 of heating chamber 7 and time period t2 until humiditychange detection portion 23 detects the change of 1.0 V. However, theinvention is not limited to the above, and such additional time periodmay be determined based only on one of initial temperature T0 and timeperiod t2 necessary for humidity change.

INDUSTRIAL APPLICABILITY

As in the foregoing, the cooking device according to the presentinvention is suitable for thawing and heating food in a large lump suchas frozen pilaf or frozen grilled rice balls as those sold atconvenience stores.

We claim:
 1. A cooking device, comprising:a heating chamberaccommodating food; microwave heating means for heating the food in saidheating chamber by microwaves; heater heating means for heating the foodin said heating chamber using a heater; a temperature sensor for sensinga temperature in said heating chamber; a humidity sensor for sensing ahumidity in said heating chamber; control means for making such acontrol that said food is heated by the heater heating means using theheater after said food is heated by microwaves by said microwave heatingmeans; and counter means for counting a time period from the start ofheating till the sensor output of said humidity sensor exhibits aprescribed humidity change, said control means controls said microwaveheating means to conduct additional heating before heating by heaterheating means by said microwave heating means based on the result ofcounting by said counter means and the temperature in the heatingchamber at the start of heating, sensed by said temperature sensor. 2.The cooking device as recited in claim 1, whereinsaid control meansoperates a time period for said additional heating based on the resultof counting by said counter means and the temperature of the heatingchamber at the start of said heating.
 3. The cooking device as recitedin claim 2 wherein said food is frozen precooked food.
 4. The cookingdevice as recited in claim 1 wherein said food is frozen precooked food.5. A cooking device, comprising:a heating chamber accommodating food;microwave heating means for heating the food in said heating chamber bymicrowaves; heater heating means for heating the food in said heatingchamber by a heater; a temperature sensor for sensing a temperature insaid heating chamber; a humidity sensor for detecting a humidity in saidheating chamber; first cooking course execution means for executing afirst cooking course according to which microwave heating by saidmicrowave heating means is executed from the start of heating until thesensor output of said humidity sensor exhibits a prescribed humiditychange, and then heater heating by said heater heating means isexecuted; second cooking course execution means for executing a secondcooking course, wherein additional heating is executed based on thetemperature at the start of heating sensed by said temperature sensorand the heating time period from start of heating till the output ofsaid humidity sensor exhibits said prescribed humidity change betweenthe microwave heating and the heater heating in said first cookingcourse; and selecting means for electing one of said first cookingcourse and said second cooking course.
 6. The cooking device as recitedin claim 5, whereinsaid selecting means selects said first cookingcourse if the amount of humidity change detected by said humidity sensorafter passage of a prescribed time period from the start of heating islarger than a prescribed cooking determination value, and selects saidsecond cooking course if said humidity change amount is smaller thansaid prescribed cooking determination value.
 7. The cooking device asrecited in claim 5 wherein said food is frozen precooked food.
 8. Thecooking device as recited in claim 5, further comprising an operationportion for instructing initiation of cooking and selection of cookingcourse, whereinsaid selecting means selects one of said first cookingcourse and said second cooking course in response to an instruction fromsaid operation portion.
 9. The cooking device as recited in claim 8wherein said food is frozen precooked food.